A menu bar is a graphical control element which contains Drop-down list.
The menu bar's purpose is to supply a common housing for window- or application-specific menus which provide access to such functions as opening Computer file, interacting with an application, or displaying help documentation or manuals. Menu bars are typically present in graphical user interfaces that display documents and representations of files in windows and but menus can be used as well in command-line interface programs like text editors or where drop-down menu is activated with a shortcut or combination key.
There is only one menu bar, so the application menus displayed are those of the application that is currently focused. Therefore, for example, if the System Preferences application is focused, its menus are in the menu bar, and if the user clicks on the Desktop which is a part of the Finder application, the menu bar will then display the Finder menus.
Apple experiments in GUI design for the Apple Lisa project initially used multiple menu bars anchored to the bottom of windows, but this was quickly dropped in favor of the current arrangement, as it proved slower to use (in accordance with Fitts's law). The idea of separate menus in each window or document was later implemented in Windows and is the default approach in most Linux desktop environments.
Even before the advent of the Macintosh, the universal graphical menu bar appeared in the Apple Lisa in 1983. It has been a feature of all versions of the Classic Mac OS since the first Macintosh was released in 1984, and is still used today in macOS.
The standard GNOME desktop uses a menu bar at the top of the screen, but this menu bar only contains Applications and System menus and status information (such as the time of day); individual programs have their own menu bars as well. The Unity desktop shell shipped with Ubuntu from version 11.04 through 17.04 uses a Macintosh-style menu bar; however, it is hidden unless the mouse pointer hovers over it, similar to the Amiga interface. Starting with 17.10, it defaults to the GNOME desktop environment, using its menu bar.
Other and desktop environments use a similar scheme, where programs have their own menus, but clicking one or more of the mouse buttons on the root window brings up a menu containing, for example, commands to launch various applications or to logout.
Window manager menus in Linux are typically configurable by editing text files or using a desktop-environment-specific Control Panel applet.
The Workbench screen title bar would typically display the Workbench version and the amount of free Chip RAM and Fast RAM. An unusual feature of the Amiga menu system was that the Workbench screen would display a "Workbench" menu instead of a "File" or "Apple" menu, while conforming applications would display "Project" and "Tools" menus ( projects and tools being, respectively, the Amiga terms for what in other systems are called files or documents, and programs or applications).
Keyboard shortcuts could be accessed by pressing the "right Amiga" key along with a normal alphanumeric key.
Power users would often switch off the always-on menu, leaving it to be displayed at the mouse pointer's location when the right mouse button was pressed. The same implementation is used by GNUstep and conforming apps, though applications written for the host operating system or another toolkit will use the menu scheme appropriate to that OS or toolkit.
Microsoft-style bars are physically located in the same window as the content they are associated with. However, Bruce Tognazzini, former employee of Apple Inc. and Human–computer interaction professional, claims that the Mac OS's menu bars can be accessed up to five times faster due to Fitts's law: because the menu bar lies on a screen edge, it effectively has an infinite height — Mac users can just "throw" their mouse pointers toward the top of the screen with the assurance that it will never overshoot the menu bar and disappear.
This assumes that the desired menu is currently enabled, however. If another application has "focus", the menu will belong to that application instead, requiring the user to check and see which menu is active before "throwing" the mouse, and often perform an extra step of focusing the desired application before using the menu, which is completely separate from the application it controls. The effectiveness of this technique is also reduced on larger screens or with low mouse acceleration curves, especially due to the time required to travel back to a target in the window after using the menu. On systems with multiple displays, the menu bar may either be displayed on a single "main" display, or on all connected displays. The classic Mac OS, and versions of macOS prior to OS X Mavericks displayed only a single menu bar on the main display; Mavericks added the option to show the bar on all displays.
Some applications, e.g. Microsoft Office 2007, Internet Explorer 7 (by default), and Google Chrome and Mozilla Firefox 4 in Windows and Linux, have effectively removed the menu bar altogether by hiding it until a key is pressed (typically the "alt" key). These applications present options to the user contextually, typically using to select actions.
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